This invention relates to providing power to a device over a network transmission medium.
Network devices, such as personal computers (xe2x80x9cPCsxe2x80x9d) and IP (xe2x80x9cInternet Protocolxe2x80x9d) telephones, traditionally received power from wall outlets. Such devices have additional wiring to connect them to the wall outlets. In some configurations, this can be inefficient, particularly for devices that are connected to networks via transmission media, such as Ethernet, that are capable of transmitting power with little or no adverse effect on network data. Systems were therefore developed for providing power to a device over Ethernet wiring.
Not all devices, however, can withstand application of power via Ethernet wiring. In devices that are not configured to accept power via Ethernet, receipt of power via Ethernet can cause damage to circuitry in the devices.
Accordingly, in one aspect, the invention features a method which determines if a device can accept power over a network transmission medium, and which provides power to the device over the network transmission medium if it is determined that the device can accept power over the network transmission medium. By determining whether the device can accept power before applying the power, the invention reduces damage caused by improper application of power.
This aspect of the invention may include one or more of the following features. Determining if the device can accept power over the network transmission medium includes sensing if there is an overcurrent condition in the device and/or sensing if the device is receiving power from another source. The method determines if the device can accept power by supplying an initial power pulse to the device over the network transmission medium, determining whether the device can handle additional power based on the initial power pulse, and supplying a test power pulse to the device over the network transmission medium if the device can handle the additional power. The initial power pulse may be shorter than the test power pulse.
The method determines if the device can handle the additional power by sensing an amount of current that is absorbed by the device in response to the initial power pulse, and determining whether the device can handle the additional power based on the amount of current that is absorbed by the device. The amount of current that is absorbed by the device is sensed using a resistor that is coupled in series with the network transmission medium.
The method may include receiving an indication, in response to the test power pulse, that the device can accept power over the network transmission medium. The indication may comprise a link status bit that is transmitted from the device. The method may store data indicating whether power is being supplied to the device. The power provided to the device may be controlled by a remote network device. The network transmission medium may comprise an Ethernet line.
Other features and advantages will become apparent from the following description and the claims.